Question: Solve for $z$ : $z - 4 = -20$
Answer: Add $4$ to both sides: $ \begin{eqnarray} \\ z - 4 &=& -20 \\ \\ {+4} && {+4} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-4 + z} &\hphantom{=}& \hphantom{-20} \\ z &=& -20 {+ 4} \\ \end{eqnarray} $ Simplify. $ z = -16$